Compressor or turbine blade manufacture

ABSTRACT

A turbine or compressor blade holding fixture and machining method contemplates the subassembly of all the blades upon the rotor of the compressor or turbine. Fixture rings along with radial biasing members in the form of annular o-rings are intersecured to opposite sides of the blades so as to radially position the latter in their normal &#34;running position&#34; while so mounted on the rotor of the wheel. In such condition all of the blades may be simultaneously machined such that the outer tips thereof lie on a true uniform, desired outer diameter to provide subsequently uniform tip clearance to the surrounding shroud when mounted in a gas turbine engine for operation.

TECHNICAL FIELD

This invention pertains to improved apparatus and method formanufacturing compressor and turbine wheels as utilized in gasturbomachinery.

BACKGROUND OF THE INVENTION

One class of compressor or turbine wheels, such as utilized in gasturbine engines, includes a plurality of compressor or turbine bladesmounted to the outer periphery of a central rotor. It is important ingas turbomachinery that the outer tips of the compressor or turbineblades run very closely to surrounding shrouds to minimize gas leakageacross the tips of the blades. Machining of such turbine or compressorblade tips to the desired outer true tip diameter is a difficultmanufacturing operation because the blades are normally contained withroot portions loosely fitting within dovetail grooves in the rotor atthe periphery thereof. Compensation for manufacturing tolerance buildupalso hampers manufacture of such a compressor or turbine wheel to assureall blade tips are disposed at a uniform, small tolerance from thesurrounding outer shroud.

SUMMARY OF THE INVENTION

Accordingly, an important object of the present invention is to providean improved method for machining such compressor or turbine blade outertips while the turbine blades are all mounted within the associatedrotor and affixed at locations simulating their running position whensubsequently assembled and utilized in a gas turbine engine.

More particularly, the present invention contemplates such a methodwhich includes an assembly fixture that engages each of the turbineblades and uniformly radially biases each radially outwardly to theirnormal "running" position, i.e. the position they attain while operatingin a gas turbine engine. The fixture holds the blades in such locationwith sufficient force to allow machining of the tips of all the bladesin a unitary operation. More particularly, the method contemplatesmounting the assembled rotor and blades along with the holding fixtureson to a lathe for uniform, simultaneous cutting of the blade tips to thedesired outer diameter.

The present invention accomplishes these objects by utilizing a pair ofring fixtures mounted at opposite sides of the wheel rotor and axiallyintersecured to one another. Resilient biasing members between each ofthe rotors and an exposed, underside portion of the platform of each ofthe blades urges the blades outwardly into the "running" position.Additionally, an axial biasing member may be included to urge the bladeseach uniformly axially onto a datum face for simulating the axiallocation of all the blades in their "running" position.

These and other objects and advantages of the present invention arespecifically set forth in or will become apparent from the followingdetailed description of the preferred embodiment of the invention, whenread in conjunction with the accompanying drawings.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a partial perspective view of a segment of a compressor orturbine wheel with the blades mounted thereon;

FIG. 2 is an elevational cross-sectional view of the arrangementillustrated in FIG. 1 and showing the fixturing members for locating theblades in their "running" positions; and

FIG. 3 is a perspective illustration of the assembled blades, rotor andassembly fixtures as mounted upon a portion of a lathe for machining.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now more particularly to the drawings, a typical axial turbineor compressor wheel is generally denoted by the numeral 10 and includesa central rotor 12 having a central through bore 14, an outer periphery16, and a plurality of dovetail configured grooves 18 extending axiallythrough the rotor and disposed generally near the periphery 16.Compressor or turbine blades 20 are carried upon the outer periphery ofthe rotor 14. Each compressor or turbine blade 20 includes a radiallyupstanding airfoil 22 having an outer tip 24, a platform 26, and a rootportion 28 which is complementary contoured to be received within thedovetail groove 18. Each blade 22 is assembled upon rotor 12 byinsertion axially into the dovetail groove 18. The dovetailconfiguration of groove 18 radially secures the blade, but in theposition illustrated is relatively loosely mounted therein. Loosemounting is necessary not only to facilitate assembly, but also to allowfor necessary tolerances because of differential thermodynamic responsesbetween the blade and rotor during the operation of the wheel.

As so mounted upon the rotor 12, the blades 20 are not necessarilydisposed in the "running" location, i.e. the positions the blades takewhile spinning within the gas turbine engine. Further, the diameter ofeach of the tips 24 relative to the center of the rotor 12 varies due tomanufacturing tolerance buildups.

As clearly illustrated in FIG. 2 the present invention contemplates afirst ring fixture 32 which is disposed axially on one side of the rotor12 and associated blades 20. This first ring fixture 30 is denoted asbeing on the "forward" axial side of the wheel for reference purposesherein. A second, similar ring fixture 32 is disposed on the opposite"aft" axial side of the rotor 12 and blades 20. Each of the ringfixtures 30, 32 have a plurality of stepped faces which are disposedtoward the opposite axial sides of the blades 20 and rotor 12. Forexample, fixture 30 has an axially extending wall 34 and a radiallyextending wall 36 disposed adjacent the portion of platform 26 whichprotrudes axially forwardly from the rotor 12. Similarly, fixture 32 hasan axially extending circular wall 38 and a radially extending circularwall 40 which face the portion of platform 26 which protrudes in an aftdirection from the rotor 12. The second fixture 32 further preferablyincludes another groove which receives a resilient elastomer 42.

Importantly, the present invention contemplates resilient biasingmembers in the form of annular o-rings 44, 46 which may be of circularcross-section. O-ring 44 is disposed between walls 34, 36 and theforwardly protruding portion of platform 26. O-ring 46 is disposedbetween walls 38, 40 and the aft protruding portion of platform 26. Thefixture in FIG. 2 further includes a plurality of bolts 48 receivedthrough aligned openings 50, 52 in the fixtures 30 and 32 forintersecurement thereof. Each bolt 48 passes loosely through anassociated hole 54 in the rotor 12.

When so assembled as illustrated in FIG. 2, the axial intersecurementaffected by tightening of bolts 48 causes squeezing of the o-rings 36and 46 in the grooves in which they are received. This creates axial andradial forces on each of the blades 20 to uniformly radially urge eachof the blades outwardly to the "running position" that the blades willsubsequently assume during operation of the wheel in a gas turbineengine. Additionally, the resilient elastomeric member 42 acts upon theaft protruding portion of platform 26 to urge each of the blades 22axially against the radial face 36 of the first fixture 30. Radial face36 is premachined to act as a datum face such that when the blades areurged against this datum they assume their "running" axial positionrelative to the rotor 12.

In this manner, the axial compression and intersecurement of the tworing fixtures 30 and 32 creates a generally uniform radial outwardpressure on all of the blades 20 to securely hold them in their"running" position. This uniform radial force prevents blade cocking.

Since the blades 20 are now securely held in their "running" positionsupon the rotor 12, the entire subassembly with fixtures may now beutilized for true tip machining of the blade tips 24. More particularlythe blades 20, as assembled on to rotor 12 with the fixtures 30, 32 andbolts 52 all intersecured, may be affixed as a unit on a lathe asillustrated in FIG. 3. In FIG. 3 a lathe fixture 55 and portion ofassociated spindle 56 rotatably mounts the subassembly on the normalrotational axis of the wheel 10. By conventional lathe grinding andcutting, during spinning of the assembly illustrated in FIG. 3, the tips24 of all of the blades 20 may be machined to the desired outer truediameter in a single, unified operation.

From the foregoing it will be apparent that the present inventioncontemplates an improved method of machining compressor or turbine bladeouter diameters or blade tips 24 which includes the step of looselyassembling the annular array of blades 20 on the outer periphery of therotor with platform portions 26 of each of the blades 20 protrudingaxially forwardly and aft from opposite sides of the rotor 12. Ringfixtures 30, 32 are mounted to opposite sides of rotor 12 and axiallyintersecured to one another by bolts 48 so as to axially fix and locateblades 20 by urging them against the datum provided by face 36 onfixture 30. A generally circumferentially uniform, radially outwardforce is then applied to the protruding portions of platforms 26 of eachof the blades so as to radially position and fix all of the blades 20.Subsequently, the outer tips 24 may be machined with the blades 50 fixedin both a radial and axial direction.

The foregoing detailed description of the preferred arrangement of theinvention should be considered exemplary in nature and not as limited tothe scope and spirit of the invention as set forth in the appendedclaims.

Having described the invention with sufficient clarity that thoseskilled in the art may make and use it, what is claimed is:
 1. A methodof machining compressor or turbine blade outer diameterscomprising:loosely assembling an annular array of blades upon the outerperiphery of a rotor, with platform portions of the blades protrudingaxially forwardly and aft from opposite sides of the rotor; mountingfirst and second ring fixtures on the opposite sides of the rotor;axially intersecuring the ring fixtures to axially fix and locate theblades; applying a generally circumferentially uniform radially outwardforce to the protruding platform portions of the blades to radiallyposition and fix the blades; and machining the outer tips of the bladeswhile so axially and radially fixed.
 2. A method as set forth in claim1, wherein said applying step includes compressing a first resilientbiasing member between the first ring fixture and the forwardlyprotruding platform portions, and compressing a second resilient biasingmember between the second ring fixture and the aft protruding platformportions of the blades.
 3. A method as set forth in claim 2, whereinsaid first and second biasing members are O rings.
 4. A method as setforth in claim 3, wherein the axially intersecuring step comprisesbolting the first second ring fixtures together with a plurality ofbolts passing loosely through axial holes in the rotor.
 5. A method asset forth in claim 4, wherein the axially intersecuring step includesresiliently biasing the blades to urge the forwardly protruding platformportions thereof axially into engagement with a radially extending datumface on the first ring fixture.
 6. A method as set forth in claim 5,wherein the blades are axially biased by a third resilient memberextending between the second ring fixture and the aft protrudingplatform portions of the blades.
 7. A method as set forth in claim 1,wherein said assembling step comprises inserting root portions of theblades into complementary configured, generally axially extendingdovetail grooves at the periphery of the rotor.
 8. A method as set forthin claim 1, wherein said machining step includes mounting the blades,rotor and first and second ring fixtures as unit upon a rotor lathe.